1. Field of the Invention
The present invention relates to an intermediary transfer apparatus and a fixing apparatus which are used for an image forming apparatus such as a copier, and an image forming apparatus using the intermediary transfer apparatus and the fixing apparatus, and more particularly to a technology for thermally fixing images with an electrophotographic image forming apparatus.
2. Description of the Related Art
With a conventionally known electrophotographic type image forming apparatus having a fixing apparatus, an image is formed, typically, by conveying a recording medium (e.g. paper) having an unfixed toner (toner image) transferred thereon while heating the unfixed toner (toner image). One particularly known exemplary image forming apparatus transfers an image from an image carrier (e.g. photoconductor) to a recording medium via an intermediary transfer member (e.g., intermediary transfer belt). In each transfer process using the foregoing image forming apparatuses, the quality of the transferred image and/or steady transfer performance may be affected by factors such as image deviation caused from speed differences for conveying the target image, and dryness and thickness of the recording medium.
Accordingly, in one conventional example, toner on an intermediary transfer member is simultaneously transferred and fixed by directly heating and pressing the toner onto a recording medium. For example, as shown in Japanese Patent Registration No. 3042414 and Japanese Laid-Open Patent Application No. 7-225524, a technology where a heating member is disposed in a manner stretching an intermediary transfer member at its inner peripheral surface for pressingly heating a toner from the inner peripheral surface.
In another conventional example, a secondary transfer technique is proposed, in which toner, instead of being heated at an intermediary transfer member, is heated from an outer side after being transferred from the intermediary transfer member to a fixing member.
Nevertheless, in the above-described example where the toner is heated from the inner peripheral surface constantly at the contacting portion between the heating member and the intermediary transfer member, the entire area of the intermediary transfer member is heated to a high temperature, thereby requiring a time to cool for contacting the image carrier at which developing is performed. In order to attain a cooling performance, the intermediary transfer member is required to extend its peripheral length. This results to forming the apparatus with a large-sized body. Further, adding a cooling member for attaining the cooling performance increases component manufacture cost. Further, heating the intermediary transfer member to a predetermined temperature leads to an increase in the rise time of the apparatus.
Furthermore, spaces between the transfer target recording media are also subjected to heating since the intermediary transfer member is constantly heated. This is a disadvantage from an energy saving aspect. The heat radiation from the highly heated heating member and the intermediary transfer member causes the temperature inside the image forming apparatus to rise, and may lead to generation of unsatisfactory images due to, for example, toner fused onto the image carrier.
Furthermore, with the secondary transfer technique, since a portion of the fixing member on which toner is not disposed is heated more than a portion of the fixing member on which toner is disposed, the intermediary transfer member becomes heated by contacting the fixing member. Although the increase in the temperature of the intermediary transfer member is relatively subtle that the toner or photoconductor may not be damaged during transfer to the fixing member or the transfer from the photoconductor to the intermediary transfer medium, such temperature rise may eventually accumulate enough energy to cause a large amount of damage.
In another conventional example, a technology is proposed in which temperature rise of the intermediary transfer member, the fixing member, and the inside of the apparatus is restrained by selectively heating only a portion where an image is not fixed, for generating steady, high quality images. In order to execute this technology, a non-contacting heating unit for heating the toner is mainly employed. This, however, requires usage of a toner containing an infrared absorbing agent for absorbing radiant energy, thereby restricting the use of bright colors and the reproduction of colors. Furthermore, although a contacting heating unit may be employed for executing the selective heating procedure (e.g. contacting a heating member with a fixing roller), this may cause the surface of the fixing roller to easily wear away.